As electrically conductive thick film pastes, metal powder and glass frit dispersed to an organic binder and solvent, as necessary, are well known. The metal powder and glass frit are printed on a substrate such as a ceramic substrate or the like, having an excellent heat resistance baked at about 600.degree. to 900.degree. C. to form a thick film electric conductor. Suitable metal powder for such use includes gold powder, silver powder, platinum powder, silver-palladium powder, copper powder, and the like.
The metal powders previously used in thick film pastes, e.g., gold powder, platinum powder, silver powder, silver-palladium powder, silver-plated composite powder have the following defects. The noble metals, such as gold, platinum, silver, silver-palladium and the like, are very expensive; silver tends to cause electromigration; and silver-palladium has inferior electroconductivity. Electroconductive pastes using copper powder encounter other problems; that the electroconductivity thereof is lowered due to oxidation caused while they are preserved; the pastes tend to oxidize when baked; the atmosphere in which the pastes are baked is difficult to control and thus the yield of the pastes is bad. Further, electroconductive thick film pastes using silver-copper alloy powder composed mainly of silver and dispersed in an organic vehicle together with glass frit are disclosed [Japanese Patent Kokai (Laid-Open) SHO 62 (1987)- 140304]. The disclosure describes that silver-copper alloy powder containing 72 wt % of silver can be baked at 600.degree. C., but this alloy is expensive because it contains a large amount of silver, and there is a tendency toward electromigration of silver.
Silver-plated copper powder is disclosed to reduce the amount of precious metal required [for example, Japanese Patent Kokai SHO 52 (1977)-71531], but this power involves problems that when the copper powder is made into paste, silver is exfoliated, electromigration occurs and electroconductivity reproduction is difficult.